The present invention relates generally to a method and apparatus for diagnosing failure in an idle switch installed in an internal combustion engine. The idle switch is provided to detect and indicate the fully closed state of a throttle valve installed in a throttle chamber in an intake passage of the internal combustion engine.
An activation signal derived from the idle switch indicative of the fully closed state of the throttle valve is an essential factor to indicate that the idling engine is and to determine the correct amount of fuel to be fed to the engine when it is idling or decelerating with the throttle valve closed.
Hence, when such failures as insufficient contact or a broken line in the idle switch occur, proper control of the fuel injection quantity becomes impossible and accordingly undesirable exhaust gas components increase. In addition, the driver of the vehicle in which the engine is mounted cannot easily notice such kinds of failure.
Recently, the demand for a self-diagnosis system by which self-diagnosis for such kinds of failures can be carried out to indicate presence of such failures or to store information indicating the presence of such failures in a memory so as to simplify inspection and repair has been felt.
A Japanese document titled "M-TEU engine service manual" published on January, 1984 by Toyota Jidosha kabushiki kaisha exemplifies the above described diagnosing apparatus.
In the above-identified Japanese document, a full open switch which turns to ON and generates an On signal when the throttle valve is in a fully open state is used and the idle switch diagnosing apparatus indicates that the idle switch has failed if both ON signals of the idle switch and full open switch are simultaneously received.
However, the above-described idle switch diagnosing apparatus cannot clearly distinguish the failure of the idle switch from that of the full open switch. In addition, it cannot diagnose the condition of the idle switch when the idle switch cannot generate the ON signal because it is not being operated or there is a broken line in the idle switch.